As an extension of the principle investigator's (PI) research on the effects of stress on species-typical behavior, the proposed project examines behavioral and psychopharmacological reactions in rats to laboratory and ethological stressors. Specifically, the effects of exposure to electric shock will be compared with those effects produced by the following series of natural stressors: (a) defeat from a dominant male conspecific, (b) attack by a lactating female rat, and (c) predatory threat by a cat. The behavioral reactions to these stressors and the contextual control exerted by their respective fear odors will involve the use of the PI's published method of recording freezing and burying responses to a wall prod that is a source of subsequent shock. The possible attenuation of contextual fear, associated with the various stressors, will be tested by providing safety-signal feedback concerning the termination of the stressor or deflation of fear via extinction. Possible opioid mediation of these behavioral reactions will be determined by administering opiate antagonists either prior to the stressor or during later prod-shock tests with fear odors either present or absent. Finally, the above stress, contextual-fear, and opioid-blocking procedures will also be employed to determine whether they each alter previously reported stress-induced enhancements of analgesic and withdrawal reactions to exogenous morphine. This combination of behavioral and physiological experiments should provide important information about the effects of a range of laboratory and ethological stressors, and their associated stress odors, on species-typical defense reactions and on the interaction of morphine with endogenous pain-regulating systems. Hopefully, this research will provide the basic design and methodological procedures to determine whether other analgesic drugs (e.g., PCP) and stress-sensitive stimulants (e.g., amphetamine, cocaine) will show enhanced reactions when organisms are exposed to various types of natural stressors and later experience biologically- related stress odors.